Quantitative MRI using STrategically Acquired Gradient Echo (STAGE): optimization for 1.5 T scanners and T1...

Area of Science:

• Magnetic Resonance Imaging
• Quantitative Imaging
• Medical Physics

Background:

• The Strategically Acquired Gradient Echo (STAGE) protocol, initially developed for 3T MRI scanners, enables rapid acquisition of quantitative maps like T1, T2*, proton density, and quantitative susceptibility mapping (QSM).
• Widespread clinical use of 1.5T MRI scanners necessitates adapting advanced imaging protocols for this lower field strength.

Purpose of the Study:

• To adapt and optimize the STAGE imaging protocol for 1.5T MRI scanners.
• To evaluate the accuracy and repeatability of T1 estimates derived from the optimized STAGE protocol at 1.5T.

Main Methods:

• Optimized flip angles (FA) for 1.5T using simulations and phantom/in vivo data to maximize signal-to-noise ratio and T1 precision.
• Assessed T1 accuracy by comparing STAGE-derived values against inversion recovery sequences in both phantom and in vivo datasets.
• Evaluated scan-rescan and physiological variability using coefficient of variation (COV) from repeated scans on a single subject and a group of 27 subjects.

Main Results:

• Optimal flip angles (FA1,2 = 7°,38°) were identified for 1.5T STAGE imaging.
• T1 estimate errors were below 3% for phantom and 5% for in vivo measurements.
• Scan-rescan repeatability (COV: 0.8–2%) and physiological variability (COV: 1.8–4.8%) were found to be low.

Conclusions:

• The optimized STAGE protocol provides accurate and repeatable T1 mapping and other quantitative maps in approximately 7 minutes on 1.5T scanners.
• This adaptation makes the STAGE protocol a practical tool for clinical settings utilizing 1.5T MRI.
• The study establishes a foundation for investigating the clinical applications of STAGE imaging at 1.5T.